Project #3: Zona Pellucida Binding Proteins In Sperm Egg Interactions Reproduction is a complex and multifactorial process, and hundreds of mammalian genes have already been identified to function in reproduction. The binding of spermatozoa to the cumulus oophorus, the egg zona pellucida, and eventually the egg plasma membrane are essential steps for the future fusion of gamete genomes and the initiation of the zygote organization. As might be expected, both sperm and egg proteins play active roles in the initial and subsequent interactions of sperm and eggs. Many of the proteins that play key or supporting roles from binding of sperm to the zona pellucida until entry of the sperm DNA into the egg cytoplasm are largely unknown. Our overlying hypothesis is that the two zona pellucida binding proteins are critical mammalian sperm proteins in one or more of these steps in fertilization. The Specific Aims are: 1) Study ZPBP1:ZPBP2 binding and sperm-egg interactions in vitro; 2) Generate and analyze mice lacking ZPBP1, ZPBP2, or both; and 3) Determine whether men with defective binding of their sperm to eggs have mutations in ZPBP1 or ZPBP2 genes or additional candidate genes. These studies will be important for understanding the key proteins and mechanisms involved in sperm:egg interactions in vivo and will help to define essential proteins implicated in human male infertility.